1. Field of the Invention
The invention relates to a spring-loaded contact probe used to provide electrical contact between electrical components, such as between testing equipment and an electrical device under test (DUT) or between any two electrical components of an assembly.
2. State of the Art
Electronic devices such as circuit boards and integrated circuit devices are tested after they are manufactured to verify that all required electrical connections have been properly completed and that all electrical components are performing properly. The DUT is coupled to a DUT board using a contactor. The DUT board is coupled to a testing machine. Spring-loaded contact probes are often used in the contactor to provide electrical contact when sending or receiving test signals from the DUT board. The spring-loaded probes, also known as pogo pins, are housed in sockets and formed in an array to simultaneously provide contact between the DUT and the DUT board. The array of pogo pins is aligned with the targeted test contacts of the DUT. The pogo pins are formed of conductive material to provide an electrical connection between the DUT and DUT board.
A pogo pin typically includes a barrel type housing having an axially movable probe therein, the probe having a pin-shaped end on one or both ends thereof. Pogo pins are typically mounted in an array in a substrate and may be removed to allow replacement of the probe. Typically, one end of the movable probe extends in one direction of the contact pads of a device under test while the opposite end of the probe extends toward the contact pads of a substrate. Within the barrel type housing, the probe may resiliently slide axially within the housing having at least one spring biasing the probe within the housing. The spring acts to resiliently bias the probe for maintaining the tips in contact with a device under test and a portion of the substrate. Typically, during testing, one end of the probe is retained by engaging a contact pad or ferrule in an aperture in the substrate, compressing the spring resiliently biasing the probe within the barrel type housing, while a device under test is pulled or moved down to engage the other end of the probe through the use of any of several known apparatus using either vacuum, pneumatic or mechanical actuation or any combination thereof, to further resiliently bias the probe within the barrel type housing and increasing the amount of force acting upon the substrate.
A problem with the conventional pogo pin is the damage to the contact pads or ferrules of the substrate from the repeated contacting of the lower tip of the probe and portions of the substrate. The cyclical motion of the repeated contacts causes fretting, a form of contact degradation. Fretting of a contact may cause oxidation products or wear debris in the interface, or frictional polymer formation. This creates shorting problems, reducing the reliability connection. The contact pads then must be repaired or replaced due to the damage.
Accordingly, there is a need for a pogo pin which reduces fretting and improves the reliability of the contacts and, therefore, the reliability of the connection during use of the pin. A pogo pin which isolates the connection between the lower end thereof and the contact pad on a substrate from cyclical forces is desired.
An improved double-headed test probe provides for isolating the contacts of a substrate from the forces caused by contacting the upper tip to each semiconductor device. Springs controlling the movement of each tip are isolated from one another by means of a feature attached to the barrel of the test probe. This isolated spring design may also be used when retrofitting existing sockets or contactors.